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Darwin Correspondence Project

From J. S. Burdon Sanderson   12 May [1874]1

The Brown Institution, | Wandsworth Road, S.W.

May 12

Dear Mr Darwin,

We have made comparative experiments as to the relative digestibility of fibrin & gluten, on the same plan as those we made before, of which I have written the results on the next page. They shew that gluten is much more difficult to digest than fibrin.2

I propose tomorrow to try after subjecting gluten to digestion, there is any remainder i.e—whether gluten contains any indigestible constituent, for it must I think be regarded as a mixed substance

Dr Klein3 will tell you what he has observed in the bones we have digested

Very truly yours | J B Sanderson

Two comparative experiments were made with the same digestive liquid, one with fibrin the other with gluten, each lasting four hours as in the previous series.

The digestive liquid contained 8.8 of pepsin-extract & 6.4 of hydrochloric acid in 1000 C.C. of water. The quantities digested in each case were

Fibrin 0.2815
Gluten 0.1150

Hence the quantity of gluten digested was to that of fibrin as 40.8 to 100.4

CD annotations

1.1 We have … digested 3.1] crossed pencil
Top of letter: ‘Gluten’ pencil; ‘(1)’ red crayon


The year is established by the relationship between this letter and the letter to J. S. Burdon Sanderson, 14 May 1874.
For the results of Burdon Sanderson’s experiments with fibrin, see the letter from J. S. Burdon Sanderson, 30 March [1874].
These experiments were reported in Insectivorous plants, p. 118.


Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Reports results of experiments comparing digestibility of gluten and fibrin for CD’s work on Drosera.

Letter details

Letter no.
John Scott Burdon Sanderson, 1st baronet
Charles Robert Darwin
Sent from
Brown Institution
Source of text
DAR 58.1: 51–2
Physical description
ALS 3pp †

Please cite as

Darwin Correspondence Project, “Letter no. 9456,” accessed on 5 June 2023,

Also published in The Correspondence of Charles Darwin, vol. 22